High pressure syringes have been used in medical procedures for many years. To facilitate single hand retraction and injection motions, a high pressure syringe is typically designed with thumb and hand rings or grips to allow sufficient hand control in both the injection (depression of plunger) and the aspiration (retraction of plunger) modes.
Injection of radiopaque dye solutions into the human body during diagnostic and therapeutic cardiovascular procedures is one application which would employ a high pressure syringe. These procedures are conducted millions of times each year. The purpose of the procedure is to momentarily displace blood with the radiopaque dye so that the details of the fluid filled vessels may be captured by radioimaging on film or screen.
Generally, radioimaging is done more frequently and elaborately during diagnostic procedures, where mapping of the anatomy is required for further evaluations. But dye injection is also needed during therapeutic procedures, such as angioplasty, in order to enable the physician to evaluate catheter location, condition of the lesion, nature of the stenosis, progress of the procedure, effectiveness of the dilatation, and location and orientation of stent placement, if necessary.
During an angiography or angioplasty procedure, the interventionalist uses a hand-held syringe to inject a sufficient volume and flow rate of radiopaque dye to opacify the artery under study. Inadequately opacified vessels generally result in overestimation of stenosis severity due to contrast “streaming” as it forms a layer with unopacified blood. The specific volume and rate of injection is controlled by the interventionalist by observing the fluoroscopic image. For instance, in the right coronary artery, 3–6 cm3 of contrast are injected at a rate of 2–3 cm3 per second, and in the left coronary artery, 4–7 cm3 are injected at the same rate.
To generate this critical volume/flow dynamic through a narrow catheter lumen using viscous radiopaque dye, syringe pressures of 100 psi or more are often required. Such high pressure delivery is critical to create the appropriate contrast filling. If the dye is delivered with insufficient injection pressures, inadequately opacified vessels can result causing either incorrect fluoroscopic images or repeat injections. Repeating the injection subjects the patient to a higher risk of adverse side effects of the radiopaque dye and also increases the cost of the procedure. A major reason for inadequate injection volumes is the limitations on current syringes to deliver the necessary pressure, especially with users who do not possess above average hand strength.
In the past, the focus in newly designed syringes was on increasing injection pressure by increasing a user's ability to generate greater hand forces. Finger and hand grips have been made as ergonomically comfortable as possible to allow muscle leverage to generate maximum hand squeezing forces. Designs such as U.S. Pat. No. 4,925,449 (hereinafter “'449”) and U.S. Pat. No. 5,554,132 have focused on improving the hand grips to achieve maximum gripping power. The '449 patent disclosed a shortened syringe plunger stroke to allow the plunger to fit within the operator's palm in an attempt to maximize the force that the hand could exert.
In addition, U.S. design Pat. Des. No. 289,434, U.S. Pat. No. Des. 320,276, and U.S. Pat. No. Des. 325,437 show high pressure syringe designs which emphasize ergonomically designed finger and thumb grips. None of these designs attempt to solve the basic problem of high force/high volume requirements inherent in the procedure. As a result, there is a clear need for an fresh approach to this problem.
It is well known that syringe injection pressure is calculated as the ratio of hand force to plunger cross section area.Syringe Pressure=Hand Force/Plunger Area (or barrel internal cross-section area)
One commercially available high pressure syringe (Merit Medical, model CCS460) provides increased injection pressure by reducing the barrel cross-sectional area. However, due to the traditional design of the syringe, this decrease in the barrel's cross-sectional area requires a reduction in syringe volume from 10 cubic centimeters to 6 cubic centimeters to maintain a plunger stroke length that is ergonomically acceptable. This lower volume is undesirable in most interventional procedures.
It is also well known that small diameter tuberculin syringes with an injection volume of about 1 cubic centimeter can generate substantial injection pressures. But again, the small injection volume is inadequate for many procedures requiring high pressure injections.
Neither ergonomic refinements or reduced syringe barrel cross-sectional areas have provided a device which delivers the pressures and volumes necessary for the medical uses described above, while reducing the amount of force needed from the syringe user.
To provide high delivery pressures while reducing the force provided by the user, one must reduce the barrel's cross-sectional area. To maintain the needed delivery volume, one must increase the stroke length. However, existing syringe design has already reached the maximum stroke length usable by the average hand. In the present invention, a unique syringe design allows an increased stroke length within the ergonomic limitations of the average hand in conjunction with a lowered barrel cross-sectional area, thereby reducing the force required from the user without reducing delivery pressure or volume.